The Mukhya Upaniṣads

Māṇḍūkya · Om and the Four Quarters of the Self

Mantra 10

स्वप्नस्थानस्तैजस उकारो द्वितीया मात्रोत्कर्षादुभयत्वाद्वोत्कर्षति ह वै ज्ञानसन्ततिं समानश्च भवति नास्याब्रह्मवित्कुले भवति य एवं वेद ॥ १० ॥

In plain words

Taijasa, whose field is dream, is the second sound-unit U, because of elevation or intermediacy. One who knows thus elevates the continuity of knowledge, becomes even-minded, and has no one ignorant of Brahman born in the family.